Antigen-specific T cell responses are an essential component in antitumor immunity. Definition of immunodominant tumor antigens recognized by T cells has been a very important endeavor in cancer immunology for two reasons. First, direct molecular identification of T cell recognized antigens is a critical first step in understanding and further delineating the relationship between the immune system and the endogenously arising cancers. Second, the identification of shared immunodominant tumor antigens will provide the basis for development of antigen-specific vaccines as well as other forms of T cell mediated cancer immunotherapy. While much emphasis has been placed on the study of MHC class I restricted CD8 antitumor responses and antigens recognized by CD8+ CTL, relatively little is known about the MHC class II restricted CD4 antitumor response and tumor antigens recognized by CD4 cells. GM-CSF transduced tumor cell vaccines represent an effective means of activating both CD4+ and CD8+ T cells. In order to further define CD4+ recognized antigens and CD4 responses in human cancer, we have analyzed renal cancer patients vaccinated with autologous GM-CSF transduced tumor vaccines that have generated strong DTH responses against their tumor post-vaccination as well as clinical responses. We have successfully cultured tumor specific CD4+ T cell clones from two patients. Some of the clones within the panel recognize antigens uniquely expressed by the autologous tumor while others recognize antigens shared by multiple renal tumors. We propose to identify the antigens recognized by these CD4 cells and study immune responses against them. Specifically, we propose to: 1) Utilize biochemical approaches to identify and characterize both unique and shared renal cancer antigens recognized by clones within our panel. 2) Study responses specific for the identified CD4 recognized renal cancer antigens within PBL from renal cancer patients pre- and post-vaccination and 3) Construct IgG-MHC class II-peptide chimeras as a means of directly staining antigen specific CD4 T cells and utilize these constructs to follow antigen specific CD4 responses.